Fault-tolerant large area Active Matrix Liquid Crystal Displays (AMLCDs) are useful for flight-critical, primary aircraft cockpit displays where safety and high reliability are of the utmost importance for both military and commercial aircraft platforms. However, the desired fault tolerance presents significant challenges.
U.S. Pat. Nos. 7,295,179 and 7,728,788 both present possible approaches to fault tolerance through simple redundancy. U.S. Pat. No. 7,295,179 describes a liquid crystal display with two identical but totally electrically isolated left and right side displays residing on one single glass substrate. Under this arrangement, if a fault occurs in one side of the composite display (in one of the displays), the other side will still be operational. Thus, in this arrangement, the two displays can be driven to appear as one display and if one of the displays fails, the failing display is simply turned off and the other display continues (but with now only half of the total display area of the two displays working together). So in essence, a fault in the left or right (or top or bottom) portion of the composite display can be isolated to the left or the right (or top or bottom) portion and does not render the entire display unusable.
The approach put forward in U.S. Pat. No. 7,728,788 partitions the liquid crystal display into multiple sections which are driven by independent sources. Fault tolerance is achieved somewhat in that if one section fails, the remaining section(s) can remain operational.
Unfortunately, if a fault occurs in the above solutions, typically there will some amount of the original (display) information lost, even though the display system might yet still display enough information for the flight crew to return home safely.
Moreover, military and commercial aircraft cockpit displays often incorporate many fault detection capabilities which may trigger actions within a fault tolerant system in an attempt to mitigate the effects of the fault, thereby improving the overall reliability of the system. However, in the case of a display system where a fault occurs within the Active Matrix Liquid Crystal Display (AMLCD) itself or within its associated video path to the AMLCD, then that fault is usually only detectable by a visual inspection of the display by the operator, if at all.